Apparatus for expanding holes

ABSTRACT

A hole expander for use in conjunction with well bore drill strings which has a tool body defining a cylinder, an axially movable piston disposed in the cylinder, and a skirt portion secured to the piston. A plurality of radially arranged arms have one end secured to the tool body and another end adapted to receive cutting tools such as rotary cone cutters or abrasive cutters that are pivotal about axes transverse to an axis of the cylinder and are movable in an axial direction over a predetermined distance. Sides of the arms adjacent the skirt portion have a configuration to engage the skirt portion. When the piston moves axially in response to pressure being applied to the cylinder, the arms pivot outwardly relative to the axis of the cylinders. An intermediate skirt engaging surface of the sides of the arms is angularly inclined relative to the axis of the cylinder and engages an end of the skirt portion. When the arms are farthest removed from the cylinder in an axial direction the intermediate skirt-engaging surfaces of the arms are disposed adjacent the free ends of the skirt portion of the cylinder and bias the skirt portion, together with the piston, in a direction towards the cylinder. When the cylinder is fully extended a skirt-engaging surface of the arms engages a periphery of the skirt and locks the arms in an outwardly projecting position.

United States Patent [72] lnventors Bruce J. Cordary LosAlamitos; PaulJ. Arnerich, Fountain Valley, Calif. [21] AppLNo. 796,778 [22] FiledFeb.5,l969 [45] Patented Apr. 20, 1971 [73} Assignee The Servco CompanyLong Beach, Calif.

[54] APPARATUS FOR EXPANDING HOLES '9 Claims, 4 Drawing Figs.

[52] U.S.Cl 175/268 [51] lnt.Cl ..E21b43/l6 [50] FieldofSearch 175/263,267,268

[5 6] References Cited UNITED STATES PATENTS 2,754,089 7/l956 Kammerer175/268 2,799,479 7/1957 Kammerer.... 175/268 2,822,149 2/1958 Kammerer175/267X 2,922,627 l/1960 Kammerer l75/267X Primary Examiner David HBrown Attorney-Christie, Parker & Hale ABSTRACT: A hole expander for usein conjunction with well bore drill strings which has a tool bodydefining a cylinder. an axially movable piston disposed in the cylinder,and a skirt portion secured to the piston. A plurality of radiallyarranged arms have one end secured to the tool body and another endadapted to receive cutting tools such as rotary cone cutters or abrasivecutters that are pivotal about axes transverse to an axis of thecylinder and are movable in an axial direction over a predetermineddistance. Sides of the arms adjacent the skirt portion have aconfiguration to engage the skirt portion. When the piston moves axiallyin response to pressure being applied to the cylinder, the arms pivotoutwardly relative to the axis of the cylinders. An intermediate skirtengaging surface of the sides of the arms is angularly inclined relativeto the axis of the cylinder and engages an end ofthe skirt portion. Whenthe arms are farthest removed from the cylinder in an axial directionthe intermediate skirt-engaging surfaces of the arms are disposedadjacent the free ends of the skirt portion of the cylinder and bias theskirt portion, together with the piston, in a direction towards thecylinder. When the cylinder is fully extended a skirt-engaging surfaceof the arms engages a periphery of the skirt and locks the arms in anoutwardly projecting position.

PATENTED APRZO [an SHEET 8 BF Q APPARATUS FOR EXPANDING HOLES BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates torotary well bore tools and more particularly to rotary well bore toolsfor enlarging diameters of intennediate portions of the well bore.

2. State of the Prior Art In the drilling of wells such as oil wells,portions of the bore below the surface must often be enlarged forvarious reasons, such as to enable the packing of the bore with gravel.Frequently the upper portions of the bore are provided with steel casingthrough which any expanding hole drill apparatus must be lowered. It istherefore necessary to retract the drilling apparatus to a diameter lessthan the diameter of the upper portion of the well bore or the innerdiameter of the well casing. Upon arrival of the hole enlargingapparatus at the desired depth, it is expanded to the desired diameterand the enlarging or underreaming operation can commence.

In the past, underreaming tools of various configurations have beenextensively used. All include pivotal arms which are retracted into atool body while the apparatus is being raised or lowered through thenarrow portions of the drill bore and which can be pivoted outwardlyrelative to an axis of the apparatus. Because of the relatively largeforces required to expand the drill arms, hydraulic actuators areusually coupled with the arms by means of linkages. Alternatively, thearms have been provided with inclined surfaces which project into a pathof the hydraulic actuator and are engaged by it upon its actuation. Thisengagement pivotally forces the arms outwardly to the larger diameter.

Upon termination of the drilling operation, the arms must be retracted.To enable the retraction, an axial force must be applied to the pistonof the hydraulic actuator to return it to its original position.

In the prior art, the pistons were'returned to their original positionin one of two ways. First, the apparatus was provided with helicalcompression springs which acted against the piston and biased it into anoriginal position against the force to which the hydraulic pressuresubjected it. Upon release of the pressure, the spring moved the pistonaxially into its original position. The second class of underreamers isprovided with double-acting pistons which are subjected to a pressureforcing the pistons into their original position upon termination of thedrilling operation. This embodiment is frequently employed inconjunction with relatively large size underreamers.

SUMMARY OF THE INVENTION The present invention provides apparatus forenlarging subsurface holes, such as well holes. Briefly, it includes atool body adapted to be secured to a drill string and defining acylindrical bore having an open end. Another end of the bore is closedand in flow communication with a fluid carrying portion of the drillstring. A piston is axially movable in the bore and includes a skirtportion extending past the open end of the bore. Means are provided forcommunicating an interior space of the cylinder confined by the pistonwith the exterior of the tool body. A plurality of radially spaced armsare adapted to mount cutting tools adjacent one end of the arms forengaging a portion of the hole to be enlarged. The arms are disposedexteriorly of the bore and are freely movable parallel to an axis of thebore over a predetermined distance. Furthermore, they are pivotal aboutan axis transverse to the axis of the bore adjacent another end of thearms proximate to the piston. The amrs have a configuration to engagethe skirt portion when the piston moves towards the open end of the boresuch that the ends of the arms are pivoted outwardly relative to theaxis of the bore in opposition to a pivotal force from their weight.When the cutting tools are disengaged from the portion of the hole beingenlarged, they engage an end of the skirt remote from the piston andbias the skirt and the piston axially away from the open end of thebore. Stop means limit the outward pivotal movement of the arms.

Preferably, the tool body includes an elongated flange adjacent eachside of the arms and a shaft for pivotally and axially movably mountingthe anns in a slot of the flanges.

The underreaming apparatus of this invention eliminates the need for ahelical compression spring or a double-acting piston to return thepiston to its original position. Instead, the piston is biased into itsoriginal position by the outwardly extending arms. The arms includefirst, second and third skirtengaging surfaces which respectivelyposition the arms adjacent the axis of the cylinder when the piston isin its original position; pivot the arms outwardly relative to the axisabout the shaft; and position the arms in an extended position so thatthe ends adapted to receive the cutting tools are remote from the axisof the cylinder. The third surface is in engagement with the skirtportion during the drilling or underreaming operation when an axialforce moves the arms to a position closest to the interior space definedby the bore. Upon termination of the underreaming, the apparatus islifted whereby the arms move axially in an opposing direction away fromthe interior space under their weight. This axial movement is sufficientto place the free end of the skirt portion adjacent the angularlyinclined second skirt-engaging surface of the arms. An axial componentforce, resulting from the pivotal bias of the arms under their ownweight about the shaft securing it to the flanges of the tool body,biases the skirt and the piston ina direction towards their originalposition until the arms are positioned adjacent the axis of thecylinder.

Although an underreamer constructed according to the present inventioncan be constructed for underreaming any size hole, it is particularlywell adapted for use in conjunction with large diameter drill holeswhich require large underreamed sections. The relatively heavy armssubject the piston to a large axial force biasing it towards itsoriginal position.

The reduction in the number of parts required to construct theunderreaming apparatus makes it substantially more economical tomanufacture than prior art underreamers. Its simple operating mechanismassures trouble free operation of the apparatus and substantiallyenhances its service life.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary elevationalview, in section, of a hole expanding apparatus constructed inaccordance with the present invention and showing arms mounting cuttingtools in an expanded operating position in phantom lines;

FIG. 2 is a fragmentary front elevational view, in section, similar toFIG. I wherein the arms are shown in an intermediary position;

FIG. 3 is a fragmentary side elevational view of the apparatus shown inFIG. I; and

FIG. 4 is an illustration like FIG. 1 of a hole expanding apparatushaving a modified fluid flow path.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Initially referring to FIG. 1,there is shown a well bore 10 (in phantom lines) and an apparatus l2 forenlarging a portion 14 of the well bore. The apparatus is secured to adrill string (not shown) lowered through an upper portion (not shown) ofthe bore.

The apparatus I2 is described in conjunction with its application forenlarging or underreaming intermediate portions of a subterranean boresuch as an oil well bore. However, it is obvious that this apparatus canbe used for cutting and milling tubular conduits, such as oil wellcasing, by interchanging cutting tools secured to the apparatus. Theapparatus of the present invention is therefore not intended to, and isnot limited to the underreaming of subterranean drill holes. Rather itis adapted for use in conjunction with all rotatory drilling, boring,cutting, milling, etc. tools which require an apparatus capable ofexpanding its working surfaces from a lesser to a greater diameter.

The underreaming apparatus I2 includes a tool body 16 adapted to besecured to an upper drill string (not shown). It defines a cylinder 18having an open end 20, an axially movable piston 22 disposed within thecylinder, and a plurality of pivotally mounted arms 24 and 24. An end 26of the arms farthest removed from cylinder 18 is adapted to receive aconventional cutting tool which may be a conventional rotary cone cutter28, a cutter provided with an abrasive surface (not shown) for cuttingthrough tubular conduits, or cutter adapted for other applications. Thecutting tools are not further described herein since they do not fonn apart of this invention.

In the presently preferred embodiment, the tool body I6 is defined by acircular end flange 30 which is coaxially secured to the cylinder 18 andprojects past a periphery 32 of the cylinder. A face 34 of the endflange opposite face 36 adjacent the cylinder, mounts a tubular member38 which is provided with a suitable thread engaging portion (not shown)adjacent its end (not shown) remote from the end flange for securing theapparatus 12 to a lower end of a drill string (not shown).

Preferably, a tubular core 40 is secured to face 34 of the end flangeand projects through a hole 42 in the flange past side 36 into a spacedefined by the cylinder 18. An end of the core remote from the endflange includes radial projections 44 and a plurality of relief slots 46which extend from that end toward the end flange a distance which isslightly greater than the thickness of the piston. The core furtherincludes a recessed hole 48 adjacent the end provided with the radialprojections 44 and, disposed in that hole, an axially-movable generallycone-shaped plug 50 provided with seal ring 52 on a cylindrical portionof the plug. An upper end of the plug includes a spearhead 54 connectedwith a pull cable 56 extending upwardly past the tubular member 38 andthe upper drill string (not shown) to the surface of the bore.

The piston 22 disposed within cylinder 18 has a coaxial center bore 58engaging a periphery of the tubular core 40. A suitable seal ring 60seals an interior space 62 defined by end flange 30, cylinder I8, andpiston 22 from the exterior of the tool body. One or more holes 63communicate the interior space with the tubular member 38. The cylinderincludes a preferably annular protrusion 64 adjacent the center bore 58to space a face 66 of the piston from face 36 of the end flange 30 whenthe piston is in an original position adjacent the end flange. A sealring 68 is disposed about a periphery of the piston adjacent walls ofcylinder I8 and further seals the interior space 62 from the exterior ofthe tool body.

An end of the piston remote from the end flange includes a preferablycylindrical skirt portion 70 which extends from the piston past the openend 20 of the cylinder. A free end 72 of the skirt portion is providedwith a taper 74 for purposes to be described hereinafter.

A pair of laterally-spaced elongated flanges 76 are disposed on eachside of each arm 24 or 24 and are suitably secured to face 36 of the endflange 30 and the periphery 32 of cylinder 18. The flanges extend fromadjacent the end flange past the free end 72 of the skirt and haveopposite ends 78 secured to a disc 80 such that the pairs of flanges aresubstantially rigid. The cylindrical disc suitably connects a tubularprotrusion 82 which is coaxial with the disc and an axis of thecylinder. A free end of the protrusion is provided with a threaded end84 for engaging the apparatus 12 with a lower portion of the drillstring (not shown).

Each pair of flanges 76 include a pair of slots 86 which are alignedwith each other to slidably receive a shaft 88 secured to ends 90 of thearms 24 or 24'. The anns are thereby pivotal about the axis of theshaft. They can also move in an axial direction parallel to the axis ofthe cylinder from a lowermost position (shown in FIG. I) which isfarthest removed from end flange 30 to an uppermost position (shown inFIG. I in phantom lines) which is proximate to the end flange.

Each arm includes a first skirt-engaging surface 92 immediately adjacentend 90 of the arm on the side of the arm facing towards the skirtportion 70. The first engaging surface is arranged to position an outerside 94 of the arm within an axial projection of end flange 30 toprevent interference between the narrow drill hole 10 and the arms whenthe apparatus 12 is axially moved through the drill bore. The firstengaging surface 92 is substantially parallel to a periphery of theskirt portion 70 when the arm is pivoted about the axis of shaft 88 andpositioned within the axial projection of end flange 30.

A second skirt-engaging surface 96 or 96 is joined with the firstengaging surface by a preferably arcuate transitional portion 98 andextends from the first surface toward the end 26 of the arm. The secondengaging surface is angularly inclined relative to the first surface andprojects inwardly towards the axis of the cylinder 18. Immediatelyadjacent the second engaging surface is a third skirt-engaging surface100 or 100' which is shorter than either the first or the secondengaging surface and which has an angular inclination relative to thefirst surface which is less than the inclination of the second surface96 or 96'. The exact angular inclination is a function of both thelength and the angular inclination of the second engaging surface 96 or96 and is such that when the piston, together with skirt portion 70, isaxially moved towards disc 80, and the arms have pivoted outwardlyrelative to the axis of the cylinder, the third skirt-engaging surface100 or 100' is parallel to the periphery of the cylindrical skirtportion 70 when the piston is adjacent the radial projections 44 of thecore 40, as shown in phantom lines in FIG. 1.

Joined to the third engaging surface I00 or 100 is an inner side 102 ofthe arm which defines the outline of the arm intennediate the end of thethird surface and the end 26 of the arm 24 or 24'. This inner side has aconfiguration to position the cutting tool 28 adjacent the tubularprotrusion 82, as shown in FIG. I.

The arms 24 and 24' further include stop pins 104 which preferablyprotrude from each face 106 of the arms and engage suitable cutouts 108in flanges 76 for limiting the pivotal movement of the arms about shaft88 in a direction away from the axis of the cylinder 18.

Turning now to the operation of the underreaming apparatus I2, it isfirst secured to a drill string (not shown) and lowered into a drillhole 10. After it has reached the depth where the diameter of the holeis to be enlarged, the downward movement of the apparatus is halted. Thedrill string is filled with fluid drilling mud which enters the tubularmember 38 and, through holes 63 in the end flange 30, the interior space62 of the tool body 12. Thereafter the drill string and the apparatus 12are rotated by a suitable rotatory table (not shown) on the surface ofthe well bore 10. The piston 22 is disposed in its original position,the shafts 88 of the arms are disposed at the lowermost positionfarthest removed from end flange 30, and the arms, by virtue of theirweight, are pivoted inwardly to a position where ends 26 are closestadjacent the axis of the cylinder 18.

The drilling mud is pressurized through the drill string to actuate thepiston 22 and move it axially away from end flange 30. When the end 72of the skirt portion 70 arrives at the transitional portion 98intermediate the first and second skirtengaging surfaces 92 and 96 or96', respectively, the arms are pivoted outwardly away from the axis ofthe cylinder. The free end of the skirt and particularly the taper 74 ofthe free end, slides along the second engaging surface 96 or 96. Thisimparts a pivotal force onto the arms which opposes the pivotal forceimparted upon them by their weight. The movement of the anns continuesuntil the periphery of the skirt portion 70 is disposed adjacent thethird engaging surface 100 or 100', as shown in phantom lines in FIG. I.

Simultaneously with the pivotal movement of the arms, the cutting tools28 disposed adjacent ends 26 of the arms. begin to engage the formationand commence their underreaming action. To effectively drill and expandthe hole, weight is applied to the drill string from the surface toimpart an axial force onto the cutting tools. This axial force istransmitted to the cutting tool through flanges 78 and shaft 88. Itcauses the arms 24 and 24' and the shaft 88 to move relative to theflanges 76 within the confines of slot 86 until the shafts are in theiruppermost position adjacent the ends of the slots proximate the endflange 30.

The downward movement of the piston 22 continues and the skirt portion70 is given a length such that when the shafts 86 are disposed proximateto the end flange, the third engaging surface 11M or K00 is disposed onthe periphery of the skirt portion. Additionally, the cutouts 108 of theflanges are arranged to engage the stop pins and prevent a furtherpivotal, outward movement of the arms when surface 100 or 166' abutsskirt portion 70. [n this position, the arms extend outwardly a maximumdistance.

The radial projections 44 on the tubular core 40 are arranged to engagethe piston 22 when the free end 72 of the skirt portion 70 is disposedjust beyond the end of the third engaging surface we or 100' and thearms are proximate to the end flange 30. The relief slots 46 in thetubular core now permit unrestricted circulation of drilling mud fromthe interior space 62 to the exterior of the tool body 16. Pressure inthe interior space 62 is thereby relieved. No additional axial forcesare imparted upon the piston which remains in the position adjacent theradial projections during the drilling or underreaming operation.

The resulting pressure drop in the interior space 62 as well as in thedrill string is sensed at the surface. It simultaneously communicates tothe operator that the piston has reached its lowermost position andthat, by necessity, the arms are fully extended. Moreover, as long asthe drilling operation continues and no pressure builds up in theinterior space and the drill string the operator knows that the arms arein a locked position and prevented from collapsing inwardly. Theoperator is assured that the hole is underreamed to the desireddiameter.

Drilling mud continues to be pumped down through the drill string, theinterior space 62, past the relief slots 46, and into the space exteriorof the tool body to facilitate the drilling operations and removeloosened formation to the surface. The drilling mud rises in the annularspace intermediate the drill string and the well bore or a casing (notshown) disposed therein. Upon termination of the drilling operation, thedrill string, together with the apparatus 112, is lifted off the bottomof the underreamed hole to disengage the cutting tools 28 therefrom. Theweight of the arms 24 and 24' and the cutting tools now axially movesthe arms and the shafts 88 relative to the flanges 76 in slots 86 untilthe arms are at the lowermost position. The length of this movement, andtherefore of slot 86, is sufficient to disengage the third engagingsurface 100 or 1160 from the periphery of the skirt portion 70 andengage the taper M of the free end 72 of the skirt with the secondengaging surface 96 or 96. The weight of the arms 24 or 24', togetherwith the cutters, pivotally biases the arms about the axes of shafts 86.An axial component force acting in a direction towards the end flange 30is thereby imparted on the taper 74 of the skirt portion. This axialforce moves the piston axially towards the end flange until the firstengaging surface 92 engages the periphery of the skirt portion. In thatposition, the arms are fully retracted to within the axial projection ofthe end flange and the apparatus can be axially moved through the wellbore 10 to the surface. After the drilling operation is terminated, thecable 56 is pulled to remove plug 50 from the recessed hole 46 in thetubular core 40. The drill mud in the drill string is thereby drained,and the interior space 62 is communicated with the exterior of the toolbody 16 such that no resistance force is exerted upon the piston duringits axial movement towards the end flange.

If the diameter of the enlarged portion 14 of the drill bore W issubstantially greater than the diameter of drill hole 10, the arms 24and 24' are pivoted outwardly different amounts such that some of thecutting tools 28 cut a diameter which is greater than the diameter cutby the other cutting tools. in an apparatus having, say, six cuttingtools 28 and arms 24 and 24, three of them 24 are provided with a secondskirtengaging surface 96' which is substantially longer than that of theother three. Their engaging surfaces are therefore substantially closerto the axis of the cylinder when they are in a collapsed position. Uponactuation of the piston 22, the arms 24' provided with the longer secondskirt-engaging surface 96' pivot outwardly a substantially greateramount than the other arms 24. The length and angular inclination of theengaging surfaces are arranged such that when all arms are in a fullyextended position, the cutting tools make annular cuts into theformation which have successively greater diameters to cover the fullwidth of the underreamed bore with a cutting tool. The operation of theapparatus remains identical to that described above.

FIG. 4 illustrates a hole opening apparatus adapted for use inconjunction with drilling operations requiring reverse circulation ofthe drilling mud. in reverse circulation, where the drilling mud isbrought down from the surface to the drill tool through a first annularspace intermediate a first outer drill string 121 and a second innerstring 122 and is returned to the surface through the second inner drillstring, the tubular core 40 disposed in the end flange is left open. Theexterior of the tool body is in flow communication with the interior ofthe inner string through the tubular core 40. The relief slots 46 in thetubular core are omitted such that no fluid communication between theinterior space 62-and the exterior of the tool body is possible adjacentthe center bore 58 of the piston. The first outer drill string, however,fluidly communicates with the interior space 62 through holes 63.

Included are a plurality of holes 123 extending radially through wallsof cylinder 18 and positioned so that the interior space 62 communicateswith the exterior of the tool body when the piston is adjacent theradial projections 44 on tubular core 40. The holes are connected withsuitable conduits 124 (hidden by flange 76) disposed substantiallyparallel to the flanges 76 which terminate adjacent the circular disc80. Drilling mud pumped down through the annular space between the outerand inner drill strings is then discharged adjacent the bottom of theenlarged portion 14 being drilled and returns to the surface through thehole 42 in the tubular core 40 and the inner drill string 122. Theoperation of the apparatus, namely the pivotal and axial movements ofthe arms, the axial movement of the cylinder and the axial return of thecylinder to its original position by the weight of the arms, remainsidentical to the above described operation.

We claim:

1. Apparatus for enlarging the diameter of subsurface holes comprising:

a tool body adapted to be secured to a drill string;

walls defining a bore in the tool body having an open end and anotherend in flow communication with a fluid carrying portion of the drillstring;

a piston axially movable in the bore and provided with a skirt portion;

means for limiting the axial movement of the piston in the bore;

a plurality of radially spaced arms adapted to mount cutting toolsadjacent one end of the arms for engaging a portion of the hole to beenlarged and disposed exteriorly of the bore, means for mounting thearms for free movement parallel to an axis of the bore over apredetermined distance, and pivotable about axes transverse to the axisof the bore adjacent another end of the arms proximate to the piston,means on the arms for engaging the skirt portion when the piston movestowards the open end of the bore for pivoting the ends of the armsoutwardly relative to the axis of the bore in opposition to a pivotalforce from the weight of the arms and for biasing the skirt and thepiston axially away from the open end of the bore when the cutting toolsare disengaged from a portion of the subsurface hole; and

stop means for limiting the outward pivotal movement of the arms.

2. Apparatus according to claim 1 including a member secured to the toolbody and projecting through an axial center bore in the piston to aregion in fluid communication with the exterior of the body, a fluidpassage in the end of the member projecting through the piston; themember having a sufficient length that the bore in the tool body fluidlycommunicates with the exterior of the body when the arms are fullypivoted outwardly.

3. Apparatus according to claim I wherein the tool body includes aflange adjacent each side of each arm, each pair of flanges adjacenteach arm having aligned slots engaging shaft means secured to each armsuch that the arms are pivotal about axes of said shaft means and aremovable in a direction parallel to the axis of the bore within theconfines of the slot.

4. Apparatus according to claim 3 including at least two pluralities ofarms, ends of each plurality of arms projecting outwardly from the axisof the hole a distance different from the other pluralities of arms whenthe arms are fully pivoted outwardly.

5. Apparatus for enlarging the diameter of subsurface holes comprising:

a tool body adapted to be secured to a drill string and includinghydraulic actuating means having an axially extending skirt portion;

a plurality of radially arranged arms disposed adjacent the skirtportion and adapted to mount cutting tools adjacent an end of the armsremote from the actuating means;

means for mounting the arms for pivotal movement about axessubstantially transverse to an axis of the skirt portion, and formovement parallel to the axis of the skirt portion over a predetermineddistance;

a first skirt engaging surface on each arm for positioning the end ofthe arm adjacent the axis of the skirt portion;

a second surface on each arm for engaging a free end of the skirtportion and pivoting the end of the arm in a direction away from theaxis of the tool body in response to actuation of the actuating means;

a third skirt engaging portion for positioning the ends of the armsremote from said axis;

the predetermined distance being sufficient that the second skirtengaging portion is disposed adjacent the free end of the skirt portionafter the hydraulic means have been actuated and the arms are at one endof their axial movement;

means for securing the arms to the tool body such that they arepivotable and axially movable over the predetermined distance;

stop means for limiting the pivotal movement of the arms in a directionaway from the axis of the skirt portion; and

means for limiting the axial movement of the skirt portion in responseto actuation of the actuating means.

6. Apparatus according to claim 5 wherein the means for mounting thearms includes laterally spaced flanges secured to the tool body adjacentsides of the arms and shafts connected with the flanges.

7. Apparatus according to claim 6 wherein the body defines a cylinderand the actuating means include a piston disposed in the cylinder andsecured to the skirt portion, the cylinder being in flow communicationwith a fluid carrying portion of the drill string and provided with anopening adjacent the piston to fluidly communicate an interior space ofthe cylinder with the exterior of the tool body when the free end of theskirt portion is adjacent the third engaging surface and the arms movedaxially over the predetermined distance in a direction opposite to adirection the piston moves when pressure is applied to the interiorspace.

8. Apparatus for enlarging the diameter of sub-surface holes, theapparatus comprising:

a. a tool body having:

i. an end flange adapted to secure one end of the tool body to a drillstring;

ii. a cylinder having an axis, the cylinder being adapted to be in fluidcommunication with a fluid carrying rtion of the drill string and havingone end secure to the flange and another end open; and

iii. a plurality of pairs of laterally spaced elongated flanges adjacenta periphery of the cylinder extending axially away from the end flange;

b. an axially movable piston disposed in the cylinder and including askirt portion projecting past the open end;

c. an arm disposed intermediate a pair of flanges having a free endadapted to mount a cutting tool and another end adjacent the open endofthe cylinder pivotally and axially movably secured to the flanges, theaxial movement being limited to a predetermined amount, the arms havinga first, second and third skirt-engaging portion progressivelyengageable by the skirt portion when the piston moves away from the endflange in response to a fluid pressure being applied to the cylindersuch that the arm is pivoted outwardly in response to such movements ofthe skirt portion while a free end of the skirt portion is in engagementwith the second surface;

d. means for relieving the pressure in the cylinder in response to afree end of the skirt ponion being positioned adjacent the thirdengaging surface of the arm and the arm is axially farthest removed fromthe end flange; t

e. stop means for limiting the pivotal movement of the arm in adirection away from an axis of the cylinder;

f. means for pivotally and axially movably securing the other end of thearm to the flanges; and

g. means connected with ends of the flanges remote from the end flangefor connecting another end of the tool body to a drill string.

9. Apparatus according to claim 8 wherein the means for securingcomprises a shaft disposed intermediate each pair of flanges and the armdisposed between such flanges, and a slot in each flange, the shaftbeing axially movable in the slot to pivotally and axially movablysecure the arm to the pair of flanges.

1. Apparatus for enlarging the diameter of subsurface holes comprising: a tool body adapted to be secured to a drill string; walls defining a bore in the tool body having an open end and another end in flow communication with a fluid carrying portion of the drill string; a piston axially movable in the bore and provided with a skirt portion; means for limiting the axial movement of the piston in the bore; a plurality of radially spaced arms adapted to mount cutting tools adjacent one end of the arms for engaging a portion of the hole to be enlarged and disposed exteriorly of the bore, means for mounting the arms for free movement parallel to an axis of the bore over a predetermined distance, and pivotable about axes transverse to the axis of the bore adjacent another end of the arms proximate to the piston, means on the arms for engaging the skirt portion when the piston moves towards the open end of the bore for pivoting the ends of the arms outwardly relative to the axis of the bore in opposition to a pivotal force from the weight of the arms and for biasing the skirt and the piston axially away from the open end of the bore when the cutting tools are disengaged from a portion of the subsurface hole; and stop means for limiting the outward pivotal movement of the arms.
 2. Apparatus according to claim 1 including a member secured to the tool body and projecting through an axial center bore in the piston to a region in fluid communication with the exterior of the body, a fluid passage in the end of the member projecting through the piston; the member having a sufficient length that the bore in the tool body fluidly communicates with the exterior of the body when the arms are fully pivoted outwardly.
 3. Apparatus according to claim 1 wherein the tool body includes a flange adjacent each side of each arm, each pair of flanges adjacent each arm having aligned slots engaging shaft means secured to each arm such that the arms are pivotal about axes of said shaft means and are movable in a direction parallel to the axis of the bore within the confines of the slot.
 4. Apparatus according to claim 3 including at least two pluralities of arms, ends of each plurality of arms projecting outwardly from the axis of the hole a distance different from the other pluralities of arms when the arms are fully pivoted outwardly.
 5. Apparatus for enlarging the diameter of subsurface holes comprising: a tool body adapted to be secured to a drill string and including hydraulic actuating means having an axially extending skirt portion; a plurality of radially arranged arms disposed adjacent the skirt portion and adapted to mount cutting tools adjacent an end of the arms remote from the actuating means; means for mounting the arms for pivotal movement about axes substantially transverse to an axis of the skirt portion, and for movement parallel to the axis of the skirt portion over a predetermined distance; a first skirt engaging surface on each arm for positioning the end of the arm adjacent the axis of the skirt portion; a second surface on each arm for engaging a free end of the skirt portion and pivoting the end of the arm in a direction away from the axis of the tool body in response to actuation of the actuating means; a third skirt engaging portion for positioning the ends of the arms remote from said axis; the predetermined distance being sufficient that the second skirt engaging portion is disposed adjacent the free end of the skirt portion after the hydraulic means have been actuated and the arms are at one end of their axial movement; means for securing the arms to the tool body such that they are pivotable and axially movable over the predetermined distance; stop means for limiting the pivotal movement of the arms in a direction away from the axis of the skirt portion; and means for limiting the axial movement of the skirt portion in response to actuation of the actuating means.
 6. Apparatus according to claim 5 wherein the means for mounting the arms includes laterally spaced flanges secured to the tool body adjacent sides of the arms and shafts connected with the flanges.
 7. Apparatus according to claim 6 wherein the body defines a cylinder and the actuating means include a piston disposed in the cylinder and secured to the skirt portion, the cylinder being in flow communication with a fluid carrying portion of the drill string and provided with an opening adjacent the piston to fluidly communicate an interior space of the cylinder with the exterior of the tool body when the free end of the skirt portion is adjacent the third engaging surface and the arms moved axially over the predetermined distance in a direction opposite to a direction the piston moves when pressure is applied to the interior space.
 8. Apparatus for enlarging the diameter of sub-surface holes, the apparatus comprising: a. a tool body having: i. an end flange adapted to secure one end of the tool body to a drill string; ii. a cylinder having an axis, the cylinder being adapted to be in fluid communication with a fluid carrying portion of the drill string and having one end secured to the flange and another end open; and iii. a plurality of pairs of laterally spaced elongated flanges adjacent a periphery of the cylinder extending axially away from the end flange; b. an axially movable piston disposed in the cylinder and including a skirt portion projecting past the open end; c. an arm disposed intermediate a pair of flanges having a free end adapted to mount a cutting tool and another end adjacent the open end of the cylinder pivotally and axially movably secured to the flanges, the axial movement being limited to a predetermined amount, the arms having a first, second and third skirt-engaging portion progressively engageable by the skirt portion when the piston moves away from the end flange in response to a fluid pressure being applied to the cylinder such that the arm is pivoted outwardly in response to such movements of the skirt portion while a free end of the skirt portion is in engagement with the second surface; d. means for relieving the pressure in the cylinder in response to a free end of the skirt portion being positioned adjacent the third engaging surface of the arm and the arm is axially farthest removed fRom the end flange; e. stop means for limiting the pivotal movement of the arm in a direction away from an axis of the cylinder; f. means for pivotally and axially movably securing the other end of the arm to the flanges; and g. means connected with ends of the flanges remote from the end flange for connecting another end of the tool body to a drill string.
 9. Apparatus according to claim 8 wherein the means for securing comprises a shaft disposed intermediate each pair of flanges and the arm disposed between such flanges, and a slot in each flange, the shaft being axially movable in the slot to pivotally and axially movably secure the arm to the pair of flanges. 